Field of the Invention
There are certain processes in which the weighing of an article in a rapid fashion is required and efforts have been made to satisfy this requirement. In a co-pending application, assigned to the assignee of the instant application, entitled Apparatus and Method of Determining the Mass of an Article by Measuring the Shift in the Period of Harmonic Motion, Ser. No. 073,790, and filed July 13, 1987, this problem is addressed. The scale described in said copending application has proven to be a most satisfactory scale for rapidly weighing flat articles. As the title of said co-pending patent application indicates, the principle of the invention resides in measuring the vibration of a horizontally oscillating tray and determining the weight of an article on the tray from the frequency of oscillation.
Another type of scale that produces highly accurate weighing results is a force balance transducer, sometimes referred to as a magnetic scale. In this type of scale, a tray is displaced vertically as a result of the weight of an article placed thereon and a magnetic field returns the tray to its original position. Although accuracy is obtained with such a scale, the primary drawback has been the length of time required to attain the weight. With present magnetic scales, the damping period for the scale to achieve equilibrium is extensive. Clearly, it would be advantageous to have a magnetic scale not only capable of giving accurate weight, but also capable of rapid weighing.